Nitric oxide (NO) is a colorless and odorless gas. It is an important cell signaling molecule in mammals, including humans. It is also toxic as an air pollutant emitted mainly from combustion processes in, for example, fossil fuel power stations and automobile engines. Current methods for removing nitric oxide (NO) from flue gases rely on chemical processes with the disadvantages of expensive costs due to catalysts and chemicals, high energy requirements to sustain reaction temperatures, and negative environmental impacts from waste products such as urea and ammonia.
Alternative methods have been proposed to include complicated microbial bioreactors such as the BioDeNox process, which is a multiple step process that consumes ethanol, acetate, and/or Fe(II)EDTA2− as electron donors. This process is limited by the oxidation of Fe(II) to Fe(III) by oxygen, requires energy to sustain reaction temperatures of 140° F., and has a low NO removal efficiency of 40-70%.
Previous studies on the suitability of algal species for bioremediation of nitric oxide in flue gas are limited. The results of these studies have concluded that the species tested can only sustain removal of 40-65% nitric oxide for very short periods (10-15 days). The reported mechanism for nitric oxide removal in these studies relied on the pre-autooxidation of nitric oxide to nitrate and nitrite in the media in the presence of oxygen. The algal species tested then assimilated the nitrate/nitrite as nitrogen sources. Nitric oxide itself is highly toxic to cells, and the short durations of these previous experiments (10-15 days) suggest that those algal species did not have a method to metabolize nitric oxide directly.
There remains a need for an environmentally friendly and sustainable bioremediation of nitric oxide with great NO removal efficiencies.